Here's why:

* Pollen grains are the male gametophytes of seed plants.

* Gametophytes are the haploid (half the number of chromosomes) generation of plants, responsible for producing gametes (sperm and egg).

* Within the pollen grain, the generative cell divides by mitosis to form two sperm cells.

So, the pollen grain is like a tiny, protective container for the sperm, allowing it to travel to the female reproductive structures of the plant.